1. Field of the Invention
The present invention relates to an image reader incorporated in an electro-developing type camera and an electro-developing recording medium used therein, in which medium an optical image obtained through a photographing lens system is electronically and directly recorded and developed as a visible image in a short period of time.
2. Description of the Related Art
The electro-developing recording medium per se is known. For example, Japanese Unexamined Patent Publication No. 5-2280 and U.S. Pat. No. 5,424,156 disclose one type of electro-developing recording medium comprising an electrostatic information recording medium and an electric charge keeping (or holding) medium. The electrostatic information recording medium includes a photoconducting layer and an inorganic oxide material layer, and the electric charge keeping medium includes a liquid crystal display, both of the mediums being combined to face each other with a small gap therebetween.
An electro-developing type camera using the electro-developing recording medium is also known, and is referred to as an electro-developing type camera hereinafter.
In a photographing operation of the electro-developing type camera, a voltage is applied to the electro-developing recording medium. An optical image is formed on a light receiving surface of the electrostatic information recording medium by a photographing optical system, during the application of the voltage to the electro-developing recording medium. An electric charge distribution is produced over the electrostatic information recording medium in accordance with a light intensity distribution of the optical image formed on the light receiving surface thereof. Accordingly, the intensity of an electric field acting on the liquid crystal of the electric charge keeping medium is in accordance with the electric charge distribution. Thus, the optical image is reproduced in the electric charge keeping medium as a visible image. Namely, as soon as the optical image is formed on the electrostatic information recording medium, the optical image is recorded and developed in the electric charge keeping medium.
Japanese Unexamined Patent Publication No. 5-165005 discloses another type of electro-developing recording medium. In this type medium, a structure of the electrostatic information recording medium is substantially the same as that of the electrostatic information recording medium as disclosed in the above-mentioned citations except that the inorganic oxide material layer is omitted therefrom, and that the electric charge keeping medium or liquid crystal display is a liquid-crystal-polymer composite (LCPC) using a memory type of liquid crystal such as smectic liquid crystal. Similar to the first-mentioned type of electro-developing recording medium, both the electrostatic information recording medium and the electric charge keeping medium are combined to face each other with a small gap therebetween.
Furthermore, Japanese Unexamined Patent Publications No. 6-130347 and No. 7-13132 disclose yet another type of electro-developing recording medium. In this type of medium, the inorganic oxide material layer is also omitted from the electrostatic information recording medium, and the electric charge keeping medium or liquid crystal display is also a liquid-crystal-polymer composite (LCPC) using the memory type liquid crystal. Nevertheless, both the electrostatic information recording medium and the electric charge keeping medium are integrally combined with each other through the intermediary of a transparent insulating layer without any gap therebetween.
When the electric charge keeping medium is a memory-type liquid crystal display using, for example, a smectic liquid crystal, the developed visible image can be kept therein even if the electric field is eliminated from the electro-developing recording medium. Thus, the electro-developing recording medium carrying the developed visible image can be preserved in the same manner as slides or transparency sheet films. Also, in the memory type liquid crystal display, the developed image can be erased by heating it to a given temperature. In this case, the same electro-developing recording medium can be repeatedly used for photographing.
When the electro-developing type camera as mentioned above is constructed as an electronic still video camera, there is necessarily provided an image reader for optically and electronically reading a recorded and developed image of the electro-developing recording medium.
In particular, the image reader may comprise a linear light source, a focussing optical system, and a linear solid image sensor such as a one-dimensional CCD (charge-coupled device) image sensor which are aligned with each other. The electro-developing recording medium is relatively and intermittently moved with respect to the image reader such that the electro-developing recording medium passes through a space between the light source and the focussing optical system. Namely, a developed image of the electro-developing recording medium is scanned with light rays emitted from the light source during the relative and intermittent movement of the electro-developing recording medium. The light rays passing through the developed image are focussed by the focussing optical system on a light receiving surface of the solid image sensor, in which the read image is converted into image pixel signals.
The image pixel signals obtained from the image sensor may be processed in various ways. For example, the read pixel signals may be stored in a second recording medium such as an IC memory card, a floppy disk, hard disk, or the like. Also, the read image signals may be transferred to from the camera to an external processing device such an a computer, a TV monitor, and so on.
The light source of the image reader may include an LED (light emitting diode) array, a fluorescent lamp, or the like. As with all types of light sources, it is impossible to uniformly illuminate the developed image of the electro-developing recording medium, due to a shading of the light source. Accordingly, the image pixel signals obtained from the image sensor must be subjected to a shading correction in accordance with shading characteristics of the light source.
Also, as is well known, the solid image sensor of the image reader includes a plurality of photoelectric-conversion elements such as photodiodes, but these individual elements exhibit different photoelectric-conversion characteristics. Accordingly, the image pixel signals obtained from the image sensor should be further corrected in accordance with the different characteristics of the photoelectric-conversion elements of the image sensor.
Furthermore, individual products of the electro-developing recording medium as mentioned above exhibit different transparency characteristics. In particular, a transparency characteristic of the electrostatic information recording medium and a transparency characteristic of the electric charge keeping medium varies among the individual products of the electro-developing recording medium. Accordingly, the image pixel signals obtained from the image sensor must be corrected in accordance with the different characteristics of the products of the electro-developing recording medium.
Before the corrections mentioned above can be properly carried out, correction data must be prepared on the basis of an actual measurement of the shading characteristic of the light source, the different characteristics of the photoelectric-conversion elements of the image sensor, and the different transparency characteristics of the products of the electro-developing recording medium.
Nevertheless, the correction data is relative (not absolute), because the shading characteristic of the light source, the different characteristics of the photoelectric-conversion elements of the image sensor per se, and the different transparency characteristics of the products of the electrostatic recording medium are subjected to a deviation not only due to age-deterioration of the light source and the image sensor, but also due to a change in environmental factors, especially temperature.
Thus, even if a setting or the correction data is previously carried out, a proper shading correction of the light source, a proper photoelectric-conversion correction of the image sensor, and a proper transparency correction of the electro-developing recording medium cannot be ensured.